Locally full HNN extensions of inverse semigroups

We investigate a locally full HNN extension of an inverse semigroup. A norm al form theorem is obtained and applied to the word problem. We construct a tree and show that a maximal subgroup of a locally full HNN extension acts on the tree without inversion. Bass-Serre theory is employed to obtain a g roup presentation of the maximal subgroup as a fundamental group of a certa in graph of groups associated with the D-structure of the original semigrou p.